Described below are a method and a device for classification of sound-generating processes, of sound signals which are generated for operating processes of a machine or for chemical processes of a system for example.
In most processes sound or vibration signals are generated which characterize the processes. For example gas bubbles can arise during chemical processes which give rise to sounds in the tank facilities or in pipes. Machines or machine components which in a manufacturing or production process generate characteristic sounds or vibration signals as a function of their operating status and possibly their environmental conditions represent a further example.
The analysis of measurement data of technical processes is used for purposes such as uncovering defective components. The analysis of measurement data, especially of sound-generating processes, can be undertaken by physical models or by statistical models of the respective process. These models are created as a rule at a prototype process under laboratory conditions and are used in the field, when the device is being used in a production shop for example. In such situations it can occur that the measurement data, which is obtained on the basis of sound-generating processes, is influenced by changing environmental signals, for example because of changes in room acoustics. It can also occur that the machine being investigated or the process being investigated is operating under other operating conditions or with modified machine components. If the physical or statistical models obtained from a prototype of a process are used unchanged in the field, the quality of the analysis can fall so far that no satisfactory classification of the investigated process or of the investigated machine can be achieved. Typically a defective machine part will not be correctly classified as faulty.
Thus the physical or statistical models of the process to be investigated are adapted to the changing conditions in order to guarantee a sufficient quality of analysis. If for example an operating process of a machine part is investigated, a specific characteristic of the detected sound signal can be included for classification on the basis of the sound signal generated by the machine part. A possible characteristic of the sound signal is the volume of the sound signal or of the noise signal. If the volume of the sound signal exceeds a predeterminable threshold, the investigated machine part is classified as defective and a corresponding error is signaled. If however the environmental conditions change, for example because of an additional device sited next to the machine part, for example a fan, which generates an additional noise signal, the volume level or the preselected threshold will be exceeded and a fault-free machine part will be mistakenly classified as faulty. Thus in a known method of operation setting a meaningful threshold value or classification criterion is complex and time-intensive, since under some circumstances noise signals from defective machine parts which are installed as extra parts in the machine for the purpose, must also be measured to set a suitable threshold value. A further disadvantage of this known method of operation lies in that fact that, when the environmental signals change rapidly, a necessary adaptation of the physical and statistical models often occurs too slowly, so that the necessary quality of the analysis cannot be obtained in good time.